sceiv

You may elect to tinker with the input and
output transformers so that more output can
be realized from the MRF4 33. The device
has a rated output of 12 watts. and it shouldn't
be too difficult to alter this layout.
Co nslruction
This version ofthe transceiver was mounted
in a 2- x 5- x 7- cabinet and there seemed
to be plenty ofroom foreverything except the
speaker! It was constructed using four circuit
boards. The VFO should be separate since it
is to beenclosed in its own cabinet. I opted for
separating the RF stages because it required a
heat sink. but there is no reason you should
not combine the switch stage with the receiver.
Be sure you connect RF signals from stage
to stage with small RG-17S coax cable. The
size and type of the T/R and speaker leads is
not of much concern. The photographs illustrate
the originallayout.
Bifil ar-wound coils are used at the collectors
of Q I I and Q12. Each has 10turns. Tl is
fabricated from brass stock and brass tubing
using 2 FT·50 Amidon cores. The tubing
represents one tum of wire. and the primary
is seven turns of insulated teflon wire. 1'2 is
basically the same as T l , with the exception
of using four FT-SO cores. The secondary
also contains seven turns for an approximate
impedance ratio of 7:1. See Figure 4 for
winding details.
Testing a nd Operance
Initially. use a frequency counter to set the
VFO on 20 meters and adjus! the bandspread
ofthe tuningcapacitor. If you have anoscilloscope,
check that the output signal is 24V
P-P. This signal feeds over to Q 16, which is
collector-coupled into the detector and the
diode switch so there is some mismatch of
impedance. Look for a collector signal of
O.SV P-P. This should be all that is necessary
for the initial signal. You might want to align
the receiver filter next with a signal generator
and oscilloscope. The filter itself is about 2·3
MHz wide and. sweeping frequencies across
the 20 meter band, you shouldsee a peak at 14
MHz. You shouldn' t have any trouble with
alignment if it is constructed as shown.
Connecting an antenna to the jack should
bring some CW into the speaker. Use a low
SWR antenna before actually keying down.
11K: sidetone will be heard as you key. and if
you are using an SWR or power meter in line
with the antenna, some indication should be
seen . You might couple the output with a turn
of wire around the antenna lead using the
scope probe and monitor the signal. It should
be a clean wave with no ugly stufT riding on
top. Playing with the values of the low-pass
filter may help d ear up any junk you might
sec.
I have used this rig evening after evening,
working lots of stations across the country
and overseas. You will enjoy using this simple
rig much more with an audio fi lter inserted
in the AF chain as the DX pile-ups get
hectic at times. My rig was later modified by
adding another stage of amplification after
the MAR·2 . I found that the signals are almost
overpowering and the need for AGC
32 73 Amateur Radio Tcxfay • June. 1992
arose. California is not the best state to work
DX from and the usual weak Europeans still
are heard with this rig.
If this is your firs! home-brew project, you
will be delighted with thc results and enjoy
many hours ofQRPoperation. This is a basic
transceiver and you can add on features to
better suit your needs and operation. My antenna
is a dipole located in the attic and nothing
has been too di fficult to work so I am
certain your results will be an improvement
over mine.iii
Contact Gordon Young WB6NKJ at 305 Los
Arbolitos , Oceanside CA 92054.
Receiver Board
an
,
,1
,
2,
2,
t
1
1
2
4
1,
2
4
1
t
2
1
4
1
1
11 ,L3
l4
IC'
IC2
Z1
0 1-07
Description
10 ohmresistor
220hm
39ohm
tce onm
l BO ehm
270ehm
820 ohm
1k
1.8k
2.21<
2.4k
4.71<
'Ok
56k
'OOk
330 pFsilvermica
0.01 JlF disc ceramic capacitor
0.047 IJFdisc ceramic
O.l IJFdisc ceramic
1 JlFtantalum
2.2 JlFtantalum
10 IJF tantalum
33 IlFtantalum
5·20pFvariable capacitor
10 turns (centertapped)
on a T-37-6core
10 tu rns on a FT·37 core
MAR·2 MMIC
LM386 audioamplifier IC
SRA·l mixer
2N3904 NPN nenststors
YFOboard
1 47ohm resistor
1 120 ohm
1 330 ohm
1 1k
1 10k
, 39k
2 25 pF silver mica{or glass)capacitor
1 44 pFsilver mica (orglass)
1 150 pFsilver mica
2 270 pFsilver mica
1 0.01JlF disc ceramic cecacnor
1 0.1 IJFdisc ceramic
2 tnustenteium
1 10pF variabie
1 78L08 8-volt regulator
Q8,09 2N2222 NPN transistor
010 MPF102 FET
L5 13 turns on a T-42-6toroid
L8 10 tu rns on a FT-37 core
Parts list
Swlteh board
1 68 ohm resistor
1 180 ohm
1 220 ohm
2 1k
2 2.7k
1 3.0k
1 3.9k
2 10k
7 O.Ol IJFdiscceramiccapacitor
3 O.l IJF disc ceramic
1 4.7lJftantalum
3 1N914diOdes
1 UM9401diode
1 2N2905 PNP transistor
1 2N5223 NPN transistor
1 2N2222 NPN transistor
Ll 0,Ll 1 10 tums on a FT-37 core
1,
RFAmplifier board
1
1
1
2
1
1
1
1
• 4
3
16,L7
19
n.T2
13,14
, , ,
1
Table 2. Voltage Chart
Receive Transmit
0 11 E 0 2.6
B 0 2.3
C 0 11.7
0 12 E 0 0.3
C 0 11.7
0'3 C 12.7 12.5
ICI 13 4.7 05 C 2.0 06 C 9 .3 -
014 C 0 12.0
0 1S C 0 11.7
100hm resistor
150hm
22 ohm
1000hm
270ohm
1k
3.3k
68 pFsilver micacapacitor
430 pFsilver mica
220 pFsilver mica
0.01 1Jfdiscceramic
0.1 \.IF discceramic
10IJF tantalum
12turns on a T-5().6 COfEI
10turnson a T-37-6 COfEI
See FlQure 4
10tums bifilar wound
on an FT-37 COfEI
MAR-2 MMIC amplifier
2N5109 transistor
2N3866 transistor
MRF433 powertransistor
Note: Blank PC boards are available from
FAR Circuits, 18N640 Field court, Dundee IL
60118. Price: receiver board: $4; switch
board: $3.50; RF board: $5.25; VFO board:
$3; all four boards: $1 3. Please add $1 .50
shipping perorder.